Predicting milk and forage intake of nursing calves.
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A theoretical model was developed to predict forage intake of nursing calves based on peak milk level (PML) and BW using data from 39 Holstein steer calves individually fed for 200 d with milk replacer reconstituted to equal the fat and protein contents of beef cow milk. Treatment levels were amounts of reconstituted milk allowed per day based on lactation curves, which were based on PML of 2.72, 5.44, 8.16, 10.88, and 13.6 kg/d, respectively. Chopped alfalfa hay was offered for ad libitum intake to allow maximum voluntary forage consumption in addition to the reconstituted milk. We observed that calves receiving increased amounts of milk (10.88 to 13.66 kg of milk/d at peak) consumed little forage during the first 60 d of age. Their consumption of forage was also less than those calves receiving reduced quantities of milk (2.72 to 5.44 kg of peak milk/d) at the same BW because milk intake was prioritized. The forage DMI of the calf depended on calf BW and quality of the forage. Furthermore, calf BW and forage DMI was correlated with calf milk intake. A significant (P < 0.05) relationship between total DE intake (DEI) and BW was identified. A theoretical model was developed to predict forage DMI of nursing calves based on total DEI. The total DEI was estimated using PML and BW. Equations were developed to adjust forage DMI for DE content of the forage. A sensitivity analysis using Monte Carlo simulation indicated that forage DMI of grazing, nursing calves is likely to be less than 4.26 kg/d 95% of the time and that variation in BW and PML have the greatest impact on forage DMI. We concluded that equations developed in this study can be used to evaluate different cow-calf production scenarios, including matching forage quality and availability with dam milk production potential.